Control method

Abstract

A method (50) of controlling a pitch moment of an aircraft comprises providing (54) an aircraft with a first deflector element and a second deflector element, each to influence airflow passing the tail plane surface; wherein the first deflector element and the second deflector element create a different airflow effect on the tail plane; receiving (66), as an input, a pitch moment correction value; operating (68) both deflector elements to generate a pitch moment according to the pitch moment correction value; and using one deflector element to counteract lift generated by operation of the other deflector element. The method may be implemented with primary flight control flaps, in the form of deflectors with lower mass, lower inertia and faster response time than primary flight controls.

Description

[0001] Control method

[0002] Field of the Invention

[0003] The present invention relates to a method and system configuration to control lift and pitch moment of an aircraft. More specifically, the present invention concerns the control of pitch moment generation that avoids primary elevator controls, while also providing a control mechanism to modulate lift generation to achieve controlled lift generation effects during pitch moment generation.

[0004] Background

[0005] International Patent Publication WO2018224565 A2 by the present applicant discloses a method and system for lift control of aircraft, which may be used to counter or even cancel in-flight turbulence. Appropriately controlled, the method and system allow turbulence effects to be reduced that might otherwise be experienced in aircraft cabins.

[0006] While the method of WO2018224565A2 has been successful in simulations and small aircraft test flights, there is a desire for additional / alternative means of pitch and lift control to allow the method to be implemented in a wider range of scenarios.

[0007] W02007001735A2 discloses a yaw generating system for an aerospace vehicle having a fuselage with a first portion and a second portion, and a movable control surface that can be positioned to create a flow pattern proximate to the fuselage when the aerospace vehicle is in a flow field.

[0008] US2023-0234718A1 discloses a lift augmentation system for a blown lift aircraft comprising a blown lift tailplane. Tailplane thrust-producing devices are arranged to produce a plurality of slipstreams to blow over the upper surface and the lower surface of the blown lift tailplane.

[0009] The present disclosure seeks to provide additional options for controlled pitch moment generation and lift generation.

[0010] Summary of the Invention

[0011] In accordance with a first aspect of the invention, there is disclosed a method as defined in claim 1 , of controlling a pitch moment of an aircraft, comprising: providing an aircraft with actuatable deflector elements, comprising at least one first deflector element and at least one second deflector element, upstream of a tail plane surface, the deflector elements influencing airflow passing the tail plane surface; wherein one of the at least one first deflector element and the at least one second deflector element is positioned such that its actuation creates a different airflow effect on the tail plane than actuation of the other; receiving, as an input, a pitch moment correction value; operating the at least one first deflector element to affect airflow across the tail plane thereby to generate a pitch moment according to the pitch moment correction value; and using the at least one second deflector element to at least partially counteract lift generated by operation of the at least one first deflector element.

[0012] Herein, the pitch moment of an aircraft is understood as the moment changing the pitch angle of an aircraft, i.e. whether it points upward to ascend or downward to descend.

[0013] The tail plane surface is understood to be an aerodynamic surface, such as an aerofoil, downstream of the deflector elements, typically in a rear or tail region of an aircraft. The tail plane surface may be provided by conventional stabilisers of horizontal design or V-tail form.

[0014] The controllable deflector elements are, herein, understood to be actuatable flight control units, such as flaps or other structures that are controllable to alter lift of an aircraft. Such flight control units are typically provided on, or as part of, a wing. Known deflector elements may be lift generator flaps, ailerons, slats or the like on fixed wing structures, or elevator flaps on stabilisers. The deflector elements may be provided by deformable structures, such as morphing wings. Likewise, deflector elements may be provided by thrusters, such as propeller units.

[0015] The suggestion made in this disclosure is to arrange the control of certain deflectors such that at least one first deflector is arranged to create a different airflow effect on the tail plane surface than at least one second deflector. In this way, actuation of the deflector elements, e.g. by extending, tilting, shifting, angle adjustment, blade adjustment, thrust vectoring, etc., may be used for controlled pitch moment generation.

[0016] The first and second deflector elements may be actuatable independently of each other. For instance, a first deflector element may add to, or create, a first partial airflow effect on a plane surface located behind it, such as a tail plane, and the second deflector element may add to, or create, a second partial airflow effect that may differ from the first partial airflow effect. The second partial airflow effect may be less strong or of opposite sign than the first partial airflow effect.

[0017] Herein, the airflow passing the tail plane is understood to be affected by the position and degree of actuation of the deflector elements. Operation of the deflector elements may contribute to downwash effects and / or upwash effects. By influencing the airflow in a controlled manner, downwash and / or upwash effects may be created to alter the pitch moment generated by the tail plane.

[0018] A pitch moment correction value (PMCV) will be understood as a target value or desired value, and may be set by a controller such as an autopilot system or human operator.

[0019] An appreciation underlying the aspect was that the first and second deflectors may be controlled to counteract each other’s lift effect, while contributing to a target pitch moment via downwash and / or upwash effects on the tail plane. In this manner, the method provides a possibility to create, or to contribute to, a pitch moment, without reliance on flight control elevators of a tail plane stabiliser, and in addition allowing the net lift effect to be controlled during pitch moment modulation.

[0020] The pitch moment correction value may be part of a target pitch moment value. For instance, an aircraft may use elevators as primary pitch moment generators to control the pitch of the aircraft. In addition, the deflector elements may be controlled to modulate the pitch moment according to the pitch moment correction value. The pitch moment correction value and the pitch target value may be provided as separate inputs. Alternatively, a flight controller may receive as a single input a pitch target value including the pitch moment correction value, and operate both elevators and the deflector elements of the first aspect to achieve the target value. Different feedback control loops may be provided for the primary pitch control and the deflector elements. Alternatively or in addition, the control system may be pre-calibrated, for instance with a feed-forward filter to assist with dynamic pitch adjustment, which may be implemented to reduce undesired oscillations.

[0021] As will be appreciated, the pitch moment correction value may be positive, to increase pitch angle, or negative, to decrease pitch angle. As such, a pitch moment value set by primary pitch moment generators may be further increased or reduced by the pitch moment correction value. The pitch moment correction value may be used to maintain a target pitch value when the primary flight control lacks sufficient responsiveness.

[0022] In some embodiments, the method comprises receiving, as an input, a target lift value; and operating the at least one second deflector element to generate lift according to the target lift value, taking into account lift generated by operation of the at least one first deflector element. As will be appreciated, the second deflector element may be operated while maintaining a relative deflection of the first deflector element relative to the second deflector element to generate or maintain the pitch moment according to the pitch moment correction value. It was an appreciation by the inventor that the method allows a pitch moment to be generated while modulating the degree of lift created during the pitch moment generation. E.g., the first and second deflectors may be operated to cancel each other’s lift effect, and / or to create positive or negative lift while also creating a pitch moment. By creating positive or negative lift, the overall lift of the aircraft may be increased or reduced. As such, a target lift value may be zero, or may be a positive lift value or a negative lift value.

[0023] It will be appreciated that the target lift value may be a value to be added to the lift generated by primary lift generators during normal operation of the aircraft. Likewise, the pitch moment correction value or the pitch moment may be controlled by maintaining a relative actuation of the first and second deflector elements relative to each other. This allows the pitch moment to be controlled, to generate or maintain a target pitch moment value, while using the deflector elements to generate lift.

[0024] In some embodiments, the step of providing at least one first deflector element comprises providing at least one pair of first deflector elements, one each of a pair located on opposite wings of the aircraft.

[0025] In some embodiments, the step of providing at least one second deflector element comprises providing at least one pair of second deflector elements, one each of a pair located on opposite wings of the aircraft.

[0026] In some embodiments, the method comprises simultaneously operating the at least one first deflector element and the at least one second deflector element.

[0027] In some embodiments, the method comprises providing the at least one first deflector element and / or the at least one second deflector element as deflector subassembly of a carrier flap.

[0028] Herein, a carrier flap is understood as a high-lift arrangement, such as a landing flap, comprising as subassembly one or more deflector elements, such as flaplets, that are controllable individually to be operated as first deflector element and / or second deflector element. Conveniently, but not necessarily as a requirement of all embodiments, the carrier flap is dimensioned to fit within the space, or envelope, of a conventional flap component that it is intended to replace.

[0029] The carrier flap may be configured to continue to provide the function of a conventional flap, enhanced with the capability of the first and second deflector elements. In some embodiments, the method comprises providing the at least one first deflector element and / or the at least one second deflector element as part of a leading edge high-lift control structure.

[0030] The first and second deflector elements may be provided, for instance, as part of, or in addition to, slat flight control structures, and other appropriate mechanisms.

[0031] In some embodiments, the method comprises providing the at least one first deflector element and / or the at least one second deflector element as part of a trailing edge high-lift control structure.

[0032] The first and second deflector elements may be provided, for instance, as part of, or in addition to, flap flight control structures, and other appropriate mechanisms.

[0033] In some embodiments, the method comprises providing a fixed wing tail plane surface.

[0034] The tail plane surface may be constituted by a stabiliser. The stabiliser may be a horizontal tail plane, or a V-tail (dihedral angle tail plane). However, this is not necessarily a requirement of all embodiments, and a tail plane surface may be provided by an additional tail plane surface arrangement mounted on or otherwise integrated with an aircraft.

[0035] In some embodiments, the tail plane surface has a lateral tail wing span or extension, and the method comprises providing the at least one first deflector element laterally at least partially, or completely, within the lateral tail wing span or extension.

[0036] In this manner, the main part of the downwash generated by the first deflector element, or practically all of the first partial downwash, is expected to be within the wingspan of the tail plane.

[0037] In some embodiments, the method comprises providing the at least one second deflector element laterally at least partially, or completely, outside the lateral tail wing span or extension.

[0038] In this manner, the main part of the downwash generated by the second deflector element, or practically all of the second partial downwash, is expected to bypass the tail plane. Furthermore, upwash effects may act on a tail plane, generating a pitch moment in opposite direction to the first deflector.

[0039] In some embodiments, the input is provided by one of a user, a flight controller, and / or an autopilot. In accordance with a second aspect of the invention, there is disclosed a computer program product, that, when loaded into a memory of a computer comprising a processor, executes the method according to any one of the embodiments of the first aspect.

[0040] In accordance with a third aspect of the invention, there is disclosed a flight controller for controlling a pitch moment of an aircraft, for use with an aircraft with actuatable deflector elements upstream of a tail plane surface, the deflector elements influencing airflow passing the tail plane surface; comprising at least one first deflector element; at least one second deflector element; one of the at least one first deflector element and the at least one second deflector element being positioned such that its actuation creates a different airflow effect on the tail plane than actuation of the other; further comprising an input interface configured to receive a pitch moment correction value; and being configured to allow it to operate the at least one first deflector element to affect airflow across the tail plane thereby to generate a pitch moment according to the pitch moment correction value; and to operate the at least one second deflector element to at least partially counteract lift generated by operation of the at least one first deflector element.

[0041] In some embodiments, the controller is configured to receive, as an input, a target lift value; and configured to allow it to operate the at least one second deflector element to generate lift according to the target lift value, taking into account lift generated by operation of the at least one first deflector element. The second deflector element may be operated while operating the first deflector element relative to the second deflector element to generate or maintain the pitch moment according to the pitch moment correction value.

[0042] In some embodiments, the aircraft comprises at least one pair of first deflector elements, one each of a pair located on opposite wings of the aircraft.

[0043] In some embodiments, the aircraft comprises at least one pair of second deflector elements, one each of a pair located on opposite wings of the aircraft.

[0044] In some embodiments, the controller comprises a configuration allowing it to simultaneously operate the at least one first deflector element and the at least one second deflector element.

[0045] In some embodiments, the at least one first deflector element and / or the at least one second deflector element is provided as deflector subassembly of a carrier flap.

[0046] In some embodiments, the at least one first deflector element and / or the at least one second deflector element is provided as part of a leading edge high-lift control structure. In some embodiments, the at least one first deflector element and / or the at least one second deflector element is provided as part of a trailing edge high-lift control structure.

[0047] In some embodiments, the tail plane surface is a fixed wing surface.

[0048] In some embodiments, the tail plane surface has a lateral tail wing span or extension, and wherein the at least one first deflector element is provided laterally within the lateral tail wing span or extension.

[0049] In some embodiments, the at least one second deflector element is provided laterally outside the lateral tail wing span or extension.

[0050] In accordance with a fourth aspect of the invention, there is disclosed a controller in accordance with any one of the embodiments of the previous aspect, the controller comprising a processor and software instructions implemented by the processor, the software instructions arranged to carry out the method according to any one of the embodiments of the first aspect.

[0051] One or more embodiments of the second, third or fourth aspect may comprise a configuration to carry out the methods of any one or more embodiments of the first aspect.

[0052] Description of the Figures

[0053] Exemplary embodiments of the invention will now be described with reference to the Figures, in which:

[0054] Figure 1 is a schematic plan view of an aircraft;

[0055] Figure 2 is a schematic section through a fixed wing with trailing-edge deflectors;

[0056] Figures 3 and 4 are illustrations of different actuation modes of the Figure 1 aircraft;

[0057] Figure 5 illustrates downwash effects corresponding to a Figure 3 configuration;

[0058] Figure 6 illustrates downwash effects corresponding to a Figure 4 configuration;

[0059] Figures 7A-7C illustrate a first control setting, its resulting lift and pitch moment;

[0060] Figures 8A-8C illustrate a second control setting, its resulting lift and pitch moment;

[0061] Figures 9A-9C illustrate a third control setting, its resulting lift and pitch moment; and Figure 10 shows exemplary steps of a control method. Description

[0062] Figure 1 shows a schematic plan view of a fixed wing airplane 10 constituting an aircraft. The airplane 10 comprises two fixed wings 12, here a left wing 12A and a right wing 12B, each mounted to a fuselage 14. The wings 12 are understood to provide lift, and are provided with flight controls such as flaps 17 constituting deflectable lift actuators. Operation of the flaps 17 is understood to increase or decrease lift, respectively. Flight controls may include other actuators, such as ailerons or flaperons 16.

[0063] The airplane 10 is of a type comprising a tail plane 18, here provided by a horizontal stabiliser, having a wingspan or lateral extension 19A and 19B, respectively. The stabiliser is understood to be provided with actuatable deflectors such as elevators (not shown in Figure 1) that are operable to create a pitch moment.

[0064] A suggestion made in the present disclosure is to arrange certain ones of the flaps 17 such that a first deflector element 20A of the left wing 12A is provided laterally within the lateral extension 19A of the tail plane 18, and a second deflector element 22A of the left wing 12A is located laterally outside the lateral extension 19A. Likewise, on the right wing 12B, a first deflector element 20B is located laterally within the lateral extension 19B of the tail plane 18, and a second deflector element 22B is located laterally outside the lateral extension 19B. In this manner, actuation of the first deflector elements 20A, 20B (collectively: first deflector elements 20) is understood to create a different airflow effect on the tail plane 18 than actuation of the second deflector elements 22A, 22B (collectively: second deflector elements 22).

[0065] The different airflow effect arising, here, from a different position of the deflector elements is explained using the example of downwash effects on the tail plane 18. As illustrated in Figure 4, airflow effected by operation of the first deflectors 20A, 20B, indicated as an inner downwash 24, is expected to hit the tail plane 18. Likewise, as illustrated in Figure 3, airflow effected by operation of the second deflector elements 22A, 22B, indicated as outer downwash 26, is expected to bypass the horizontal tail plane 18. It will be appreciated that the operation of the first and second deflector elements 20, 22 can be combined to vary the proportion of inner downwash 24 to hit the tail plane 18, and the proportion of outer downwash 26 to bypass the tail plane 18.

[0066] It will be appreciated that the illustrations of Figures 1 , 3, and 4 is schematic. While referring to downwash effects, it will be appreciated that the first and second deflector elements 20, 22, contribute to an increased or reduced downwash effect from the wing 12A.12B. Furthermore, in practice, and depending on flight behaviour, speed, cross airflow, and several other factors, not the entire inner downwash 24 may hit the tail plane 18. Conversely, in some configurations, some of the outer downwash 26 from a second deflector 22 may reach portions of the horizontal tail plane 18. Likewise, the configuration, size and relative position of the first and second deflector elements 20, 22, and of the tail pane 18 may affect the effect of airflow on the tail plane 18. However, for the purpose of the present disclosure, the first deflector elements 20 create a different airflow effect on the tail plane 18 than the second deflector elements 22. The second deflector elements 22 may create a stronger or less strong downwash effect, and may also create an upwash effect.

[0067] A further suggestion of this disclosure is to provide the first and second deflector elements 20, 22, as a deflector subassembly integrated with a flap carrier assembly 17, to replace a conventional flap. For instance, the flap carrier assembly 17 may be configured to fit into the envelope, or pre-assigned space, of a conventional flap. In this manner, a capability of first and second deflector elements may be retrofitted to existing wing designs. The flap carrier assembly 17 may comprise a flap component, to be operated in the manner of a conventional flap, and further comprising the first and second deflector elements 20, 22. As will be appreciated, the flight control effects of the first and second deflector elements 20, 22 are cumulative to the effects of the flap component. The flap carrier assembly 17 may be considered a high-lift flight control, and the first and second deflector elements 20, 22 may be considered secondary or auxiliary flight controls. The first and second deflector elements may be actuatable independently of the configuration of the flap component of carrier assembly 17, e.g. whether the flap component 17 is opened or fully retracted.

[0068] The integration of the first and second deflectors with a flap carrier assembly 17, as part of a flap, is believed to provide a safety feature, wherein operation of the first and second deflector elements can be overridden mechanically by control of other flight controls, e.g. by control of the carrier flap or by elevator control, for instance in response to a command by a pilot or autopilot control system.

[0069] Figure 2 illustrates a cross-section of a wing 12 comprising a wing body 12 and a flap carrier assembly 17, here showing an inner deflector element 20 actuatable under the control of a controller 30 providing signals via a data connection 28, the controller being operative to cause an actuator to actuate the inner deflector element 20 to assume a position between an upper deflection 20U and a lower deflection 20D. As such, each deflector element 20, 22 may be installed with a home position 20H, i.e. a default unactuated position partway between the upper deflection 20U and the lower deflection 20D. In this manner, the deflector elements are able to operate bidirectionally, without requiring pre-actuation. The home position will typically be at, or close to, the centre of an actuation range, although this is not necessarily a requirement of all embodiments. For instance, the home position may correspond to an extension of an aerofoil chord line. While the illustrated deflector elements are located on a wing structure of the airplane 10, they may be alternatively be located on a different carrier structure.

[0070] The flap carrier assembly 17 may comprise a locking mechanism to mechanically lock the deflector elements 20, 22 in the home position 20H, to thereby deactivate the ability to carry out pitch moment generation, if this is desired for parts of the flight operation, testing, maintenance purposes, and / or for transportation.

[0071] In a variation of the Figure 2 design, the range of the deflector element between the upper and lower deflections 20U, 20D is limited to a value not exceeding a threshold lift in comparison to the lift modulation achievable by the carrier flap 17 or maximum lift of the wing 12. To provide illustrative values, the maximum range of the upper and lower deflections 20U, 20D may be no more than a threshold lift of 25%, 15%, 10%, 5%, 2%, or no more than 1%, of the maximum lift modulation achievable by operation of the carrier flap 17 or maximum lift of the wing 12. The lift effect achievable within the deflection range is, furthermore, considered to be small relative to a lift effect achievable by other means of lift generation, such as elevator pitch control or high-lift devices. As such, the deflector elements can be designed such that their operation can practically not override the main pitch / lift generators. In this manner, an inherent safety feature can be provided to limit the lift effect of the deflector element by design to no more than a threshold lift.

[0072] Figure 5 is a schematic side view illustrating the effect expected from operating a second deflector element 22, here to generate downwash 26 bypassing a tail plane. Downstream of the second deflector element 22, there is no aircraft structure present. The actuation of the second deflector element 22 contributes to a wing lift component Lwo.

[0073] Figure 6 is a schematic side view illustrating the effect expected from operating a first deflector element 20, here to generate downwash 24 within the lateral extension of a tail plane 18, impinging at least in part on the tail plane 18. The downwash 24 contributes to a wing lift component Lwi, and also to a tail plane lift component LTP. The lift component LTP, being offset by a distance dw p, creates a pitch moment M proportional to LTP . dw p .

[0074] An appreciation underlying the invention was that, by way of the arrangement, operation of the first and second deflector elements 20, 22 can be coordinated such that lift moments Lwo and Lwi accumulate to a combined lift value, e.g. to increase lift, decrease lift, or to cancel a net lift effect from the first and second deflector elements. The combined lift value may be set to a target lift value, which in turn may be provided as an input from an operator such as a pilot, or from a flight control system such as an autopilot. The lift generation can, in this case, be combined with a pitch moment generation to also create a pitch moment M. By controlling the generation of downwash and upwash effects hitting and bypassing the tail plane, the cumulative lift contribution may be positive or negative, and the pitch moment may be positive or negative.

[0075] As such, the first and second deflector elements 20, 22 may be operated to generate a pitch moment while maintaining a degree of control over the lift generation. For instance, operation of the first and second deflector elements 20, 22 allows generation of a pitch moment without creating a net contribution to lift generation, or with a pre-determined contribution to lift generation independently of the pitch moment.

[0076] As will be appreciated, in this manner the invention enables a pitch moment generation without reliance on an elevator arrangement on the tail plane or other primary pitch moment control elements.

[0077] Figures 7 A to 7C illustrate a first control configuration 40A corresponding to Figure 3, in which a second deflector 22 is actuated without actuation of a first deflector 20. A first control signal 42 is used to operate the first deflector 20, here to not actuate and / or to maintain a rest position and / or to return to a rest position, as may be applicable. A second control signal 44 is used to operate the second deflector 22 to actuate to assume a deflecting configuration, here a downward deflection to create lift and a slight recirculation upwash effect on the tail plane, as it is located laterally outside the downwash of the first deflector.

[0078] Figure 7B illustrates an evolution over time of a lift component 42L resulting from control of the first deflector 20, here nil, and an evolution over time of a lift component 44L resulting from control of the second deflector 22. The lift components 42L and 44L amount to a cumulative lift 46, here corresponding to the lift component 44L. As illustrated in Figure 7B, the lift component 44L, and as such the cumulative lift 46, increase gradually in an initial lag region 32 until reaching a plateau 34 that may correspond to a target value.

[0079] Figure 7C illustrates a pitch moment 42P resulting from control of the first deflector 20, here nil, and a pitch moment 44P resulting from control of the second deflector 22, in a scenario in which the outer downwash 26 (Figure 3) is assumed to bypass the tail plane 18. The pitch moment 44P develops over time, comprising an initial drop 35 which can be explained as a parasitic pitch moment generated from an off-centre longitudinal position of the second deflector slightly aft of the centre of gravity. The downward actuation of the second deflector 22 creates a slight upwash effect on the tail plane that becomes pronounced at point 36, resulting in a faster rate of decline in a region 37 until the negative pitch moment stabilises at a plateau region 38. The pitch moments 42P and 44P amount to a cumulative pitch moment 48. As the contribution from the first deflector is zero, the cumulative pitch moment 48 corresponds to the pitch moment generated by actuation of the second deflector 22. The initial lag region 32 and the initial drop 35 can be explained in part by the time it takes for airflow to travel from the deflector element to the tail plane. As such, locating the tail plane and deflector elements closer to each other may reduce response time. However, a greater distance between deflector element and tail plane is expected to provide a better pitch lever effect.

[0080] Figures 8A to 8C illustrate a second control configuration 40B, corresponding to Figure 4. Here, a first deflector 20 is operated without actuation of a second deflector 22. The numerals correspond to Figures 7A to 7C, and so it will be appreciated that the cumulative lift 46 and cumulative pitch moment 48 are calculated from the contributions of the first and second deflector elements 20, 22. In the configuration 40B, the component from the second deflector element 22 is zero. Compared to Figure 7C, the cumulative pitch moment 48 of Figure 8C is stronger, and acting in the opposite direction, due to a downwash effect on the tail plane 18. The pitch moment 48 develops over time, and includes an initial drop 43 of negative pitch until a point 45 at which the downwash effect on the tail plane starts to dominate and reaches a constant level 47.

[0081] Figures 9A to 9C illustrate a third control configuration 40C, corresponding to Figure 1 . Both the first and second deflectors 20, 22 are operated simultaneously, here to counteract each other. As will be appreciated, Figure 9A illustrates a first control signal 42 to lower the first deflector element 20, and a second control signal 44 to raise the second deflector element 22. In this example, the extent of deflection is chosen such the lift components 42L and 44L cancel each other. Figure 9B shows that the cumulative lift 46 is nil.

[0082] Turning to Figure 9C, the pitch moment 42P reaches a plateau at about half the height of Figure 8C, corresponding to a less pronounced deflector actuation. The pitch moment 44P is, here, opposite (i.e., positive) compared to Figure 7C. As such, Figure 9C shows an exemplary scenario in which the pitch moments 42P and 44P amount to a cumulative net pitch moment 48 larger than zero and larger than the pitch moment 42P.

[0083] As shown in Figure 9A, the degree of deflection is not the same for the first deflector and the second deflector. This may be appropriate, for instance, if the first and second deflectors 20, 22, have different size or aerodynamic cross section. However, it will be appreciated that both deflectors can be controlled to achieve a pitch moment 48 without contributing to, or causing, a net lift 46.

[0084] The pitch moment may be positive, as shown in Figures 8C and 9C, or negative, as shown in Figure 7C. The pitch moment may be varied continuously according to a pitch moment target value and / or according to a pitch moment correction value. Likewise, if it is desired to increase or decrease lift, both the first and second deflectors 20, 22 can be controlled in a coordinated manner to achieve a cumulative lift 46 according to a target lift value other than zero, e.g. greater than zero or below zero. The cumulative lift 46 may be achieved by maintaining a cumulative target pitch moment correction value 48, by continuing to control actuation of the first deflector element 20 relative to the second deflector element 22.

[0085] The cumulative lift 46 will be understood to arise in addition to lift generated by other flight controls, particularly in addition to a primary flight control. In embodiments in which the first and second deflectors are integrated with a carrier flap assembly, the cumulative lift 46 will be understood to add to lift created by operation of their carrier flap and may be also available while their carrier flap is retracted. Likewise, the pitch moment 48 is understood to add to the pitch moment created by primary pitch moment generators.

[0086] Figure 10 shows steps of an exemplary control method 50. In step 52, an aircraft is provided with flight controls including a lift generator and a pitch moment generator. For instance, the lift generator may include flaps, flaperon and the like as part of a fixed-wing design, or may be provided by thrusters or propeller arrangements. The pitch moment generator may be provided by elevators on a stabiliser or other tail plane.

[0087] In step 54, a lift generator is provided with one or more deflector elements suitable to generate an airflow effect affecting pitch. For instance, the airflow may result in downwash hitting predominantly the tail plane.

[0088] In step 56, at least one pair of deflector elements is provided that is configured to be controllable independently, e.g. to be able to counteract its lift generation.

[0089] In step 58, the lift generator is provided with one or more deflector elements, in addition to step 54, whose operation capable of creating an airflow effect that affects pitch differently than the elements provided in step 54. For instance, the airflow may result in downwash predominantly bypassing the tail plane, or may result in upwash at the tail plane.

[0090] Steps 54 to 58 may be carried contemporaneously and / or in a different order than indicated in Figure 10. The lift generator, e.g. a wing, may be provided with integral deflector elements, for instance in the manner of morphing or deformable wing structures controllable to provide a functionality of the first and second deflector elements. In other embodiments, deflector elements may be provided by appropriately positioned thrust generators or propeller arrangements, controllable to alter airflow towards a tail plane surface. The lift generator may be provided with a subassembly or retro-fit installation. Preferably, several deflector elements are provided including one or more first deflector elements that have a first partial effect on pitch moment generation and one or more second deflector elements that have a second partial effect on pitch moment generation other than the first partial effect of the one or more first deflector elements. For instance, the first and second deflector elements may be providing differently strong pitch moments, or may be generating opposite effects. The opposite effect may be of the same magnitude to cancel each other. The deflector elements may, thereby, comprise first and second deflector elements that are able to be operated to at least partially counteract each other’s lift generation effect, and or to create a cumulative lift increase or lift reduction. Each wing of the aircraft may be provided with a pair of deflector elements capable of at least partially counteracting each other.

[0091] In optional step 60, the deflection elements are operated to generate or modulate lift only. As will be appreciated, e.g. from study of Figure 7C, actuation of deflection elements may create a pitch moment.

[0092] In step 62, the deflection elements are operated to generate or modulate a pitch moment only. With reference to Figures 9A and 9B, a pitch moment may be generated, without contributing to net lift, by coordinated control of the first and second deflector elements.

[0093] Steps 60 and 62 may be carried out several times, and may be repeated, in different order and / or simultaneously.

[0094] In step 64, the operation of the first and second deflector elements is combined to create a pitch moment while modulating the degree of lift resulting from pitch moment generation. Lift may be modulated to cancel a net contribution to overall lift, and / or to maintain a pre-determined net contribution, increase or decrease, to overall lift.

[0095] In step 66, the method includes receiving, as an input, a pitch moment correction value. The pitch moment correction value may be provided as a command e.g. from a pilot, or from an automated flight control system, such as an autopilot.

[0096] In step 68, the deflection elements are operated in response to the input received in step 66 to apply the pitch moment correction value. The pitch moment correction value may be added automatically to a pre-existing flight command. In several scenarios, the pitch moment correction value may be added in a manner avoiding a net contribution to lift. In some scenarios, it may be desirable to generate lift according to a pre-determined lift target value. In that case, the deflection elements will be understood to be operated to apply the pitch moment correction value while generating lift according to the lift target value. In this manner, a controlled increase or reduction of lift may be achieved. The pitch correction value may be a value to reduce turbulence in the manner disclosed in WO2018224565A2 by the present applicant. In this manner, the pitch correction of the present disclosure may be used in an aircraft turbulence mitigation system.

[0097] To this end, the method may be used as part of a control system configured to determine a desired vertical acceleration correction value (Aaz) and desired pitch acceleration correction value (Adq). The desired vertical acceleration correction value and the desired pitch acceleration correction value may be calculated as a difference between an expected response and a target vertical acceleration value and / or a target pitch acceleration value, the target values being received as an input via command by one of a pilot, an autopilot, a gust load alleviation system, a turbulence cancelling system, and an expected response. The expected response may be calculated taking into account flight dynamics of an aircraft, to determine a required lift correction value AL and / or a required pitch moment correction value AM to generate both the desired vertical acceleration correction value Aaz and pitch acceleration correction value Adq by actuation of the deflection elements.

[0098] As an alternative or additional use, the deflector elements may be used to provide auxiliary lift and elevator function in the event of a loss of primary lift controls and / or a loss of primary (e.g. tail) elevator control.

[0099] It is believed that the deflector elements suggested herein can be produced with smaller mass and inertia behaviour than primary flight controls. As such, it is believed that a flight controller may also be used to provide a more responsive, smoother response than primary flight controls. The arrangement disclosed herein enables a combination of differently responsive pitch control elements. It is believed that the arrangement may be employed in a coordinated pitch control system using primary pitch moment control elements, such as elevators, for low frequency pitch control, in combination with deflector elements disclosed herein for higher-frequency pitch adjustment and correction. Consequently, the operation of the deflector elements may be used in combination with primary flight controls to provide a smoother transition during operation of primary flight control elements. The smoother transition may be provided by controlled counteractuation to dampen, or partially suppress, expected overshoot responses, and / or to create smoother transition in otherwise discrete, jerky responses, and / or to create faster intermediary responses to cover lag phases of conventional flight controls.

[0100] Whilst the principle of the invention has been illustrated using exemplary embodiments, it will be understood that the invention is not so limited, and that the invention may be embodied by other variants defined within the scope of the appended claims.

Claims

CLAIMS:1 . A method of controlling a pitch moment of an aircraft, comprising: providing an aircraft with actuatable deflector elements, comprising at least one first deflector element and at least one second deflector element, upstream of a tail plane surface, the deflector elements influencing airflow passing the tail plane surface; wherein one of the at least one first deflector element and the at least one second deflector element is positioned such that its actuation creates a different airflow effect on the tail plane than actuation of the other; receiving, as an input, a pitch moment correction value; operating the at least one first deflector element to affect airflow across the tail plane thereby to generate a pitch moment according to the pitch moment correction value; and using the at least one second deflector element to at least partially counteract lift generated by operation of the at least one first deflector element.

2. The method according to claim 1 , comprising receiving, as an input, a target lift value; and operating the at least one second deflector element to generate lift according to the target lift value, taking into account lift generated by operation of the at least one first deflector element, while maintaining a relative deflection of the first deflector element relative to the second deflector element to generate or maintain the pitch moment according to the pitch moment correction value.

3. The method according to any one of the preceding claims, wherein providing at least one first deflector element comprises providing at least one pair of first deflector elements, one each of a pair located on opposite wings of the aircraft.

4. The method according to any one of the preceding claims, wherein providing at least one second deflector element comprises providing at least one pair of second deflector elements, one each of a pair located on opposite wings of the aircraft.

5. The method according to any one of the preceding claims, comprising simultaneously operating the at least one first deflector element and the at least one second deflector element.

6. The method according to any one of the preceding claims, comprising providing the at least one first deflector element and / or the at least one second deflector element as deflector subassembly of a carrier flap.

7. The method according to any one of the preceding claims, comprising providing the at least one first deflector element and / or the at least one second deflector element as part of a leading edge high-lift control structure.

8. The method according to any one of the preceding claims, comprising providing the at least one first deflector element and / or the at least one second deflector element as part of a trailing edge high-lift control structure.

9. The method according to any one of the preceding claims, comprising providing a fixed wing tail plane surface.

10. The method according to any one of the preceding claims, wherein the tail plane surface has a lateral tail wing span or extension, and wherein the method comprises providing the at least one first deflector element laterally at least partially, or completely, within the lateral tail wing span or extension.11 . The method according to claim 10, wherein the method comprises providing the at least one second deflector element at least partially, or completely, outside the lateral tail wing span or extension.

12. The method according to any one of the preceding claims, wherein the input is provided by one of a user, a flight controller, and / or an autopilot.

13. A computer program product that, when loaded into a memory of a computer comprising a processor, executes the method according to any one of the preceding claims.

14. A flight controller for controlling a pitch moment of an aircraft, for use with an aircraft with actuatable deflector elements upstream of a tail plane surface, the deflector elements influencing airflow passing the tail plane surface; comprising at least one first deflector element; at least one second deflector element; one of the at least one first deflector element and the at least one second deflector element being positioned such that its actuation creates a different airflow effect on the tail plane than actuation of the other; further comprising an input interface configured to receive a pitch moment correction value; and being configured to allow it to operate the at least one first deflector element to affect airflow across the tail plane thereby to generate a pitch moment according to the pitch moment correction value; andto operate the at least one second deflector element to at least partially counteract lift generated by operation of the at least one first deflector element.

15. The controller according to claim 14, configured to receive, as an input, a target lift value; and configured to allow it to operate the at least one second deflector element to generate lift according to the target lift value, taking into account lift generated by operation of the at least one first deflector element, while operating the first deflector element relative to the second deflector element to generate or maintain the pitch moment according to the pitch moment correction value.

16. The controller according to claim 14 or 15, comprising at least one pair of first deflector elements, one each of a pair located on opposite wings of the aircraft.

17. The controller according to any one of claims 14 to 16, comprising at least one pair of second deflector elements, one each of a pair located on opposite wings of the aircraft.

18. The controller according to any one of claims 14 to 17, comprising a configuration allowing it to simultaneously operate the at least one first deflector element and the at least one second deflector element.

19. The controller according to any one of claims 14 to 18, wherein the at least one first deflector element and / or the at least one second deflector element is provided as deflector subassembly of a carrier flap.

20. The controller according to any one of claims 14 to 19, wherein the at least one first deflector element and / or the at least one second deflector element is provided as part of a leading edge high-lift control structure.

21. The controller according to any one of claims 14 to 20, wherein the at least one first deflector element and / or the at least one second deflector element is provided as part of a trailing edge high-lift control structure.

22. The controller according to any one of claims 14 to 21 , wherein the tail plane surface is a fixed wing surface.

23. The controller according to any one of claims 14 to 22, wherein the tail plane surface has a lateral tail wing span or extension, and wherein the at least one first deflector element is provided laterally at least partially, or completely, within the lateral tail wing span or extension.

24. The controller according to claim 23, wherein the at least one second deflector element is provided at least partially, or completely, outside the lateral tail wing span or extension.

25. A controller according to any one of claims 14 to 24, comprising a processor and software instructions implemented by the processor, the software instructions arranged to carry out the method according to any one of claims 1 to 12.

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